Abstract
Dielectric relaxation spectroscopy has been used to investigate the block end-to-end vector relaxation in symmetric poly(styrene-b-1,4-isoprene) diblock copolymers both in the ordered state and in the disordered state close to the disorder-to-order transition (ODT). Evidence is presented of two new types of dielectrically active chain relaxations by approaching the ODT from the disordered state and in the ordered state. In the ordered state and besides the usual isoprene subchain overall orientation, a new block relaxation process appears with slow dynamics and amplitude that depends on the sample preparation. The slow process is related to the coherently ordered microstructure and is attributed to the relaxation of the conformal interfaces formed in the ordered state; this assignment is supported by computer simulation results. In the disordered state, a bifurcation of the single dielectric relaxation is observed; the total amplitude increases as the temperature approaches the ODT, whereas the high-frequency process shows an apparent weak temperature dependence. The fast process may be related to polyisoprene subchains that feel higher polyisoprene concentrations near the ODT, whereas the slow relaxation mode can be attributed to the induced orientation correlations near and above the ODT, as supported also by computer simulations.